Apparatus for loading toner on a developing brush

ABSTRACT

A brush for developing electrostatic latent images having apertures which enable toner particles within the core of the brush to pass through the brush onto its outer periphery. The toner is held on the outer periphery of the brush by electrical charges until attracted to the latent image by electrostatic charges.

United States Patent [72] Inventor James H. Blomk. 3.009,402 11/1961Crumrine et all 118/637 X fi 3,103,445 9/1963 Bogdonofi'et al. 118/637 X[2 A ppl- 812,797 3,262,806 7/1966 Gourge 118/637 x g' PrimaryExaminer-Mervin Stein Assi cc don Attorneys-Paul M. Enlow, Norman E.Schrader, James .1.

Wham Y Ralabate, Ronald Zibelli, Donald F. Daley and Clarence A Green[54] APPARATUS FOR LOADING TONER ON A DEVELOPING BRUSH 7 Claims, 2Drawing F131.

[52] US. Cl. 118/637 [5]] lat. 6033 13/06 1 1 Fwd sfil'dl 1 18/621ABSTRACT: A brush for developing electrostatic latent 637; 117/175images having apertures which enable toner particles within 56 the coreof the brush to pass through the brush onto its outer 1 References Citedperiphery. The toner is held on the outer periphery of the UNITED STATESPATENTS brush by electrical charges until attracted to the latent image2,959,153 11/1960 Hider 1 18/637 by electrostatic charges.

SOURCE OF AIR PRESSUR E 5/ m 1 J0 as 4 I" 1 52 J .L

J2 M G a2 6/ 0 6.! a 4d I 2 (5 I PATENTED JUL] 319m 3,592.16?

SOURCE OF AIR PRESSUR E J6 INVEN'IUR.

BY 2 54 M QZMWWMVL ATTORNEY JAMES H. BLOW JR,

APPARATUS FOR LOADING TONER ON A DEVELOPING BRUSH This invention relatesto developing latent electrostatic images on an insulating plate, and,in particular, to placing toner on the brushlike periphery of acylindrical developing brush used to develop the plate by rotating ininterference therewith.

In reproduction apparatus such as xerographic copiers a latent imageconforming to the information to be reproduced is first formed on aninsulating plate and then the latent image is made visible, ordeveloped, by the application of marking material such as a pigmented,resinous powder called toner. One method of developing the latent imageis by applying toner to it with a toner-laden developing brush.

There are various known methods and apparatus for placing toner on thedeveloping brush. One method of accomplishing this is to pass the brushthrough a toner reservoir. In this technique the toner particles arepicked up and held by the brush as it passes through the reservoir bymechanical forces and/or forces of electrostatic attraction. Althoughrelatively simple in operation, this method has an inherent difficultyin that a cavity develops in the toner as the brush rotates making itdifficult to continue to load the brush. The toner particles in thereservoir tend to become packed and stick together, especially at higherhumidities. As a result, once those particles and jacent the brush areremoved from the reservoir, the fibers on the brush no longer contactthe remaining toner particles in the reservoir since they remain packedand do not readily fall around the brush replacing the toner particlespreviously removed. An auger or some other type of mixing apparatus canbe placed in the reservoir to keep the toner from packing, but it hasbeen found such cavities still occur resulting in inefficient loading ofthe brush over a period of continuous operauon.

A second loading technique is to distribute toner particles to adeveloping brush through a screened hopper. The hopper is usuallyvibrated and placed over the brush so that the toner held inside thehopper falls through the screen, usually of fine mesh, and onto thesurface of the brush. This type of loading device has a metering problemresulting in nonuniform quantities of toner being placed on the brushwhich impairs the subsequent developing step. In addition, it isimportant that a charge of desirable polarity and uniform intensity beplaced on the toner particles before they reach the plate and this isdifficult to achieve in a hopper loading system.

Both of these loading techniques require large and cumbersome apparatusin addition to the developing brush itself to contain the toner and loadit onto the brush. Consequently, the combination of the loadingapparatus and developing brush heretofore required a large amount of thespace available within the reproduction machine and contributed to theoverall bulkiness of it. Another disadvantage of these loadingtechniques is that the developing brush must be placed withinwell-defined locations relative to the plate bearing the latent image.For instance, if the plate were in the shape of a drum which rotatesthrough various process stations in the reproduction process, and thehopper-type loading techniques were used, the developing brush could notbe placed in the vicinity of the lowest point of the drum since thetoner is loaded on the brush by gravitational forces necessitating thatthe brush be placed underneath the hopper. Similarly, if the reservoirloading technique were used, the developing brush could not be placed inthe vicinity of the highest point of the drum since the brush scoopsinto the toner reservoir during loading thereby necessitating that thebrush be placed above the reservoir.

The invention described herein overcomes the problems of loading adeveloping brush which existed in the prior art methods and apparatus.The loading technique is such that the developing brush can be placed inany location relative to the plate bearing the latent image; e.g., atany point about the periphery of the drum-type plate. In addition, theproblems of a cavity being formed by packed toner, metering the tonerflow onto the brush and adequate triboelectrification of the tonerparticles are all avoided by the present invention.

The present invention is a developing brush having a supply of tonerwhich flows from the core of the brush to its periphery. The brush is aself-contained unit which does not require a separate loading apparatusand which takes up very little space in a copier relative to the priorart devices.

Accordingly, it is an object of this invention to improve apparatus andmethod for developing latent electrostatic images by the application oftoner with a developing brush.

it is a further object to improve apparatus and method for developinglatent electrostatic images by making the overall size of the developingapparatus smaller than that of the prior art devices.

A still further object is to improve apparatus and method for developinglatent electrostatic images by loading a developing brush with tonerparticles contained within the brush.

A still further object is to improve apparatus and method for developinglatent electrostatic images by accurately metering the rate at whichtoner is placed on a developing brush.

The present invention is a developing brush having a selfcontained meansto load the periphery of the brush with toner as the brush rotatesadjacent the latent image being developed by it. Toner which iscontained within the core of the brush flows through apertures in thebrush material to the periphery of the developing brush as the brushrotates. The brush can be made of a material which generates atriboelectric charge on the toner particles as they flow through theapertures and is partially surrounded by a housing to maintain toner onits periphery in areas other than in the vicinity where the latentimages are being developed.

For a better understanding of the invention as well as other objects andfurther features thereof, reference is had to the following detaileddescription of the invention to be read in conjunction with theaccompanying drawings wherein:

FIG. I is a schematic illustration of a xerographic machine having adeveloping brush incorporating the present inven tion.

FIG. 2 is a perspective view of a developing brush incorporating thepresent invention and having portions broken away to show internalconstruction.

The present invention can be used for the developing step in any systemwhere toner particles are applied with a developing brush to a latentelectrostatic image on an insulating plate. The invention is disclosedherein principally within the environment ofa xerographic system, but itis not intended that its application be limited to this type ofreproduction system.

Referring to FIG. 1, there is shown an automatic xerographic machine.The principal element of the machine is photosensitive plate 60. Theplate has five distinct stations arranged about its periphery whichcarry out the operational steps of the xerographic process. Thesestations include charging station 10, exposing station 20, developingstation 30, transfer station 40 and cleaning station 50. The plate is inthe shape of a rotatable drum 63 which is driven about shaft 64 by amotor (not shown). The peripheral surface of the drum is covered withlayer 62, an electrically conductive material, which, in turn, iscovered on its outer surface with layer 6], a photosensitive insulatingmaterial such as vitreous selenium.

An electrostatic latent image is formed on the drum by passing itthrough charging station 10 and exposing station 20. The chargingstation consists of any suitable means for placing a uniform charge onlayer 61 such as corona charging device ll shown in the Figure. Exposingstation 20 comprises projector 21 which projects and focuses on the druma light pattern conforming to the image to be reproduced by thexerographic machine. The image projected onto the photosensitive layerof the drum is synchronized with the movement of the photosensitivelayer of the drum. The projected light pattern causes selective chargedissipation on elemental areas of layer 61, thus forming anelectrostatic latent image. Other means for forming electrostatic imagesincluding means for forming images on ordinary insulating surfaces areknown in the art and may be used instead of the one shown.

After the formation of the electrostatic latent image by passing thedrum through stations and 20, the drum carries the image to developingstation where toner particles are applied to the surface of the drum bya developing brush. As toner particles are applied to the surface of thedrum, they adhere to it according to the configuration of theelectrostatic latent image formed beforehand. The structure andoperation of the developing apparatus shown at station 30 will bedescribed in more detail below.

Following the developing step the drum carries the developed imagethrough transfer station 40 where the image is transferred from the drumsurface to support material 41. Transfer of the developed image onto thesupport material is aided by corona charging device 42 which applies anelectrostatic charge to the support material having a polarity oppositethat of the triboelectric charge on the toner particles. Transfer takesplace between guide rollers 45 which act to position the supportmaterial against the photosensitive drum at the transfer station.

Support material 41 is fed from reel 43 before transfer and is rewoundon reel 44 after transfer takes place. If support material 41 is thepermanent substrate upon which the developed image is to be fixed, asshown in the Figure, fusing device 46 can be placed along the path ofthe support material between the point where the support material isrewound on reel 44. The fusing device is positioned to heat the tonerparticles thereby permanently bonding them to the support materi al,

The final station shown in FIG. I is cleaning station 50 which comprisesa cylindrical brush Sl which contacts the photosensitive surface of thedrum. The cleaning station is utilized to remove any residue tonerparticles from the photosensitive surface after transfer occurs andbefore the surface begins a new cycle.

The above-described process and apparatus are commercially known in theart, and any of the many known equivalents of process or apparatuselements may be employed in connection with the present invention. It isintended that appropriate drive mechanisms and control circuits be apart of the general disclosure herein which would enable the continuousxerographic process to operate, however, such ap paratus is not shownsince the elements can be of any suitable design to accomplish theoperational movement of the system described above.

It is within the confines of the development station, station 30, thatthe present invention is utilized. The development station includes adeveloping brush which applies toner particles to the surface of theplate bearing the latent image by bringing the toner particles incontact with the latent image and depositing them in conformance withthe latent image. The brush can be made of any suitable material whichhas the capability of carrying toner particles to the latent image anddepositing them on the plate. For instance, a fur brush having amultitude of fibers to carry and deposit toner particles can besatisfactorily used for this purpose and is shown in the Figures. Thebrush shown consists of a backing material or pad 32 having elongatedfibers 31 protruding therefrom. Synthetic materials such as nylon,velvet, and Dynel can also be used as a brush material.

The backing material is supported by frame 36 which is mounted so thatit can be rotated adjacent the drum. Any suitable means can be used tofix the backing material onto the frame such as glue, fasteners, etc,and the frame is rotated by any suitable drive means which issymbolically depicted in FIG. 1.

The core of frame 36 is hollow so that toner particles can be placedwithin it. The brush also contains small holes or perforations 39 whichallow toner particles within the core to pass through the brush. Thetoner passes from the core to the periphery of the brush as the brushrotates due to centrifugal forces imposed on the toner particles. Sincethe toner supply is self-contained in the brush and loading of the brushoccurs through the brush due to its rotation, the development system isa very compact system where compared to the apparatus and amount ofspace required by other known systems. In ad dition, the self-containednature of the brush aliows it to be placed at any position relative tothe plate bearing the latent image. For instance, in a reproductionsystem using a rotatable drum, such as drum 63 in FIG. I, the brush canbe placed anywhere about the periphery of the drum to develop the image.Unlike other development systems, the brush is not dependent on gravityloading or collateral apparatus which limits its position in areproduction system.

The toner particles used to develop latent images are customarily finelydivided, electroscopic particles of thermoplastic resins having coloredpigments dispersed throughout. The size of the toner particles isgenerally in the range of 3 to 30 microns. in order that the tonerparticles are able to pass onto the periphery of the brush they mustflow from the core of the brush through the perforations or apertures.To assure that the toner does flow onto the brush periphery, the size ofthe apertures must be larger than the size of the toner particles, andpreferably large enough to have a continuous, uniform flow of tonerparticles to the periphery. The size of the holes also plays a role inthe amount of toner reaching the periphery of the brush over a givenamount of time. Consequently, the rate of toner passage can be meteredby preselecting the size of the holes in the brush' the larger the size,the greater amount of toner passage. The number of holes also play arole in metering. If only one hole were placed in the brush, only asmall amount of toner would flow out of the brush over a given time, butif a great many holes are placed in the brush, the rate of toner passagewould be increased manyfold. The amount of holes desirable ultimatelydepends on the amount of toner necessary to properly develop an image.

The developing brush can contain either toner particles aione or a oftoner particles and carrier beads. The carrier heads can be any suitablegranular material which has a triboelectric property which in turn willproperiy charge the toner when mixed therewith. lf toner particles aloneare placed in the core of the brush, a triboelectric charge of thecorrect polarity should be acquired by the particles before they reachthe latent image. This charge is desirable since it aids in thedeposition of toner on the plate bearing the latent image.

The toner particles can be charged in any suitable manner prior to theirbeing placed in the core of the brush or, in the alternative, canacquire a triboelectric charge as the brush is rotated after beingplaced in the brush. The latter method is accomplished through the useof mixing vanes 37 and/or charging material 38. Both the mixing vanesand charging material are made of or coated with any suitable materialwhich has a triboelectric property different than that of the tonerparticles and which will generate a triboelectric charge of desiredpolarity on the toner when the toner rubs against it. In the case of themixing vanes, a triboelectric charge is placed on the toner as the brushrotates since the vanes pass through and move relative to the toner. Thevanes also tend to keep the toner in a loose consistency which avoidspacking and aids its passage through the brush. Charging material 38 canbe used to generate a charge of the toner as the toner passes throughthe brush and onto its periphery. This material, which also hasapertures to allow toner passage, is placed adjacent the frame eitherbetween the backing material and frame or inside the frame. As tonerpasses from the core of the brush to its periphery, it must pass throughthe charging material where a triboelectric charge is placed on it. Thecharging material in FIG. 2 is shown as a mesh material to allow theeasy flow of toner. lf the toner particles are charged prior to theirbeing placed in the core of the brush, the vanes and charging materi a}would not be necessary. However, it may be desirable to keep the vanesand charging material in the brush even though the toner particles havebeen charged to make certain that all the toner particles have a uniformcharge prior to being applied to the latent image.

When the toner particles are placed in the core of the brush as part ofa developer mixture which includes carrier beads as well as tonerparticles, a triboelectric charge is generated on the toner particles asa result of their mixing with and rubbing against the carrier beads. Forthis reason the carrier bead material is chosen for its triboelectricproperty relative to the toner particles and is generally grossly largerthan the toner particles.

If a developer mixture is placed in the core of the brush, the aperturesin the brush should be smaller than the carrier beads so that thecarrier beads are always kept within its core. in this case, both impactand centrifugal forces are used to get the toner from the core to theperiphery of the brush. The impact forces are used to separate tonerfrom the carrier beads and, concurrently, centrifugal forces coerce thetoner particles through the brush to its periphery. The impact forces onthe developer are generated generally from collisions of the carrierbeads with the frame, vanes and each other. During the operation of thebrush the toner particles flow through the apertures in the backingmaterial of the brush and onto the fibers due to centrifugal and impactforces as the brush rotates, these forces causing the toner particles tomove in the direction substantially perpendicular to the backingmaterial. Since the quantity of centrifugal force varies directly withthe speed of rotation of the developing brush and since it might bedesirable to rotate the brush at relatively slow speeds under somedevelopment circumstances, it may be necessary to place an additionalforce on the toner particles to achieve a free flow of toner onto thefibers. A way of accomplishing such additional force is to introduceinto the interior of the developing brush a positive air pressure whichwould cause the particles to seek the lower pressure external to thebrush and, therefore, pass through the apertures. This air pressure canbe introduced to the core of the brush by any suitable means and isdepicted in FIG. 1 symbolically. The combination of air pressure withcentrifugal and impact forces on the particles cause a uniform,continuous flow of toner through the apertures. Provision can also bemade to replenish the supply of toner particles within the brush as theyare used to develop the latent image. Any suitable means can be utilizedfor this purpose such as introducing additional toner particles with theflow of air brought into the core ofthe brush.

Because the brush develops the latent image on the drum only at theposition where the developing brush interferes with the drum surface,i.e., in the development zone 56, provision is made for maintaining alltoner particles on the fibers of the brush until they reach thedevelopment zone. For this purpose housing 34 is used to partiallysurround the brush. It is the function of the housing to contain anytoner particles which fall off the periphery of the brush in areas whichare not in the development zone. The housing is preferably located justadjacent the path through which the ends of the fibers travel andbecause of its proximity to the brush, any particles that fall off thebrush are prevented from leaving the vicinity of the brush. Eventually,toner particles which fall off the brush are reloaded onto the brush dueto this proximity.

In addition to housing 34, a selective bias can be placed on the brushso that the toner particles remain on the brush's periphery until theyenter the development zone. This is accomplished by using a frame withconductive and relatively nonconductive elements, alternatelypositioned. As can be best seen in FIG. 2, the frame is made ofconductive elements 52 and relatively nonconductive elements 5]v Theconductive elements acquire a relatively small electrical bias in theareas outside the development zone by virtue of brushes 54 which areconnected to a suitable power source (not shown). The nature of theelectrical bias placed on the conductive elements will depend on thedevelopment mode used. For instance, if the positive-to-positivedevelopment mode is employed, the toner particles will betriboelectrically charged to a negative polarity and the bias placed onthe conductive portions of the frame will be of a positive polarity.Conversely, if the negativeto-positive development mode is employed, thebias placed on the developing brush outside the development zone will beof a negative polarity.

Although three electrical brushes 54 are shown in F 10. 2, it isintended that as many brushes be used to impose the bias on the frame ofthe developing brush as necessary to attract the toner particles to itoutside the development zone. The number of electrical brushes actuallyrequired ultimately depends on the size and number of conductiveelements used in the frame. After the toner particles pass through theapertures and onto the periphery of the brush, they tend to adhere tothe brush by virtue of their triboelectric charge and the electricalbias placed on the brush in all portions of the brush except the portionwithin the development zone. As a portion of the brush passes throughthe development zone, the electrical bias on that portion is releasedand the periphery of the brush places the toner particles adjacent toand on the drum where they are deposited in imagewise configuration. Asthat portion of the brush continues to rotate and leaves the developmentzone, more toner particles flow from the core to the periphery of thebrush to replace those particles which were deposited on the latentimage.

In addition to the apparatus outlined above, many other modificationsand/or additions to this invention will be readily apparent to thoseskilled in the art upon reading this disclosure, and these are intendedto be encompassed within the spirit of the invention herein.

What I claim is:

1. An apparatus for developing a latent electrostatic image on aninsulating surface with finely divided toner particles comprising:

a hollow, cylindrical frame capable of containing a quantity of tonerparticles and having an outer surface of brushlike material fastenedthereto with brush fibers extending outwardly from the outer surface,

apertures in the brushlike material and in the outer surface of theframe, said apertures being of a size sufficient to allow tonerparticles within the frame to pass through the outer surface to thefibers of the brushlike material,

means to support the frame in a position whereby the brush fibers extendinto contact with the insulating surface containing an electrostaticimage, and

means to rotate the frame whereby toner particles within the frame passthrough the apertures in the outer surface to the fibers of thebrushlike material and are brought into contact with the electrostaticimage on the insulating surface.

2. The apparatus in claim I further including an intermediate layer ofmaterial between the frame and brushlike material and having aperturesaligned with the apertures in the frame and brush material, saidintermediate layer of material having triboelectric properties relativeto the toner particles whereby the toner particles are triboelectricallycharged by rubbing against the intermediate layer as they pass from theframe to the brushlike material.

3. The apparatus in claim I further including a plurality of mixingvanes attached to the frame and extending into the hollow portion of theframe, said vanes being of a material which has triboelectricproperties, relative to the toner particles, whereby the toner particlesare triboelectrically charged by contact with the vanes.

4. The apparatus in claim 1 further including means to generate airpressure within the frame to urge toner particles to pass through theapertures to the brushlike material.

5. The apparatus in claim I wherein the frame comprises alternateelements of conductive and relatively nonconductive material, andfurther including a means to impose an electric field on thoseconductive elements of the frame which are located other thanimmediately adjacent the insulating surface, the electric field havingthe characteristic of placing on those conductive elements a chargehaving the opposite brush immediately adjacent the insulating plate.

7. The apparatus in claim I further including a quantity of carrierparticles within the frame which are of grossly larger size than thetoner particles and the apertures and comprise a material which hastriboelectric properties relative to the toner particles to therebytriboelectrically charge the toner particles as the frame rotates.

1. An apparatus for developing a latent electrostatic image on aninsulating surface with finely divided toner particles comprising: ahollow, cylindrical frame capable of containing a quantity of tonerparticles and having an outer surface of brushlike material fastenedthereto with brush fibers extending outwardly from the outer surface,apertures in the brushlike material and in the outer surface of theframe, said apertures being of a size sufficient to allow tonerparticles within the frame to pass through the outer surface to thefibers of the brushlike material, means to support the frame in aposition whereby the brush fibers extend into contact with theinsulating surface containing an electrostatic image, and means torotate the frame whereby toner particles within the frame pass throughthe apertures in the outer surface to the fibers of the brushlikematerial and are brought into contact with the electrostatic image onthe insulating surface.
 2. The apparatus in claim 1 further including anintermediate layer of material between the frame and brushlike materialand having apertures aligned with the apertures in the frame and brushmaterial, said intermediate layer of material having triboelectricproperties relative to the toner particles whereby the toner particlesare triboelectrically charged by rubbing against the intermediate layeras they pass from the frame to the brushlike material.
 3. The apparatusin claim 1 further including a plurality of mixing vanes attached to theframe and extending into the hollow portion of the frame, said vanesbeing of a material which has triboelectric properties, relative to thetoner particles, whereby the toner particles are triboelectricallycharged by contact with the vanes.
 4. The apparatus in claim 1 furtherincluding means to generate air pressure within the frame to urge tonerparticles to pass through the apertures to the brushlike material. 5.The apparatus in claim 1 wherein the frame comprises alternate elementsof conductive and relatively nonconductive material, and furtherincluding a means to impose an electric field on those conductiveelements of the frame which are located other than immediately adjacentthe insulating surface, the electric field having the characteristic ofplacing on those conductive elements a charge having the oppositepolarity as the polarity of the toner particles whereby the tonerparticles on the surface of the brush material at positions other thanin the vicinity of the insulating surface are urged to remain on thebrushlike material.
 6. The apparatus of claim 1 wherein the brushlikematerial comprises fur brush material having a backing pad withelongated carrier fibers protruding therefrom, and further including ahousing surrounding the brush except that portion of the brushimmediately adjacent the insulating plate.
 7. The apparatus in claim 1further including a quantity of carrier particles within the frame whichare of grossly larger size than the toner particles and the aperturesand comprise a material which has triboelectric properties relative tothe toner particles to thereby triboelectrically charge the tonerparticles as the frame rotates.